Are size and mitochondrial power of cells inter-determined?

[Display omitted] •Mitochondrion’s metabolic rate scales non-linearly with cell size.•Mitochondrion power decreases with cell size in active protists.•Mitochondria experience the highest metabolic rates in cells of smaller sizes and in intermediate-to-large cells of active protists.•Mitochondrion power is relatively independent of cell size in endogenous protists.•Mitochondrion power increases with cell size in microalgae and vascular plants. Mitochondria are the central hub of ATP production in most eukaryotic cells. Cellular power (energy per unit time), which is primarily generated in these organelles, is crucial to our understanding of cell function in health and disease. We investigated the relation between a mitochondrion’s power (metabolic rate) and host cell size by combining metabolic theory with the analysis of two recent databases, one covering 109 protists and the other 63 species including protists, metazoans, microalgae, and vascular plants. We uncovered an interesting statistical regularity: in well-fed protists, relatively elevated values of mitochondrion power cluster around the smallest cell sizes and the medium-large cell sizes. In contrast, in starved protists and metazoans, the relation between mitochondrion power and cell size is inconclusive, and in microalgae and plants, mitochondrion power seems to increase from smaller cells to larger ones (where this investigation includes plant cells of volume up to ca. 2.18 × 105 μm3). Using these results, estimates are provided of the number of active ATP synthase molecules and basal uncouplers.